This application is based upon Japanese Patent Application Nos. 2000-140554 filed on May 12, 2000, and 2001-72444 filed on Mar. 14, 2001, the contents of which are incorporated herein by reference.
1. Field of the Invention
This invention relates to a semiconductor device having a ceramic substrate on which a semiconductor element is disposed, and a heat radiating member which is fixed to the ceramic substrate so that the heat radiating member radiates heat transferred through the ceramic substrate.
2. Description of the Related Art
Recently, semiconductor devices have been required to satisfy high performance, for example, large scale integration and application of high power thereto. Accordingly, power consumption in the semiconductor devices may increase with the large scale integration and the high power application.
On the other hand, while a base plate on which a semiconductor element is disposed and a case in which the semiconductor element is contained are required to be miniaturized.
Therefore, it is difficult to radiate heat from the semiconductor device sufficiently because of the increase of the power consumption and a decrease of a radiating heat area in the device based on the miniaturization.
A prototype as shown in FIGS. 7A to 7C was studied to solve the above-mentioned problem. FIG. 7A shows a cross sectional view of a ECU (Electric Controlling Unit) for a vehicle as the semiconductor device. FIG. 7B is a cross sectional view taken along line VIIBxe2x80x94VIIB in FIG. 7A.
A ceramic substrate 21 constituting a hybrid IC (Integrated Circuit) that includes an LSI and a high power IC is disposed on a printed circuit board 25 through lead terminals 29 which electrically connect the hybrid IC and the printed circuit board 25. Moreover, the ceramic substrate 21 is fixed to a fin (heat radiating member) 23 directly. The ceramic substrate 21, the printed circuit board 25, and the fin 23 are collectively disposed in a case 24.
In this structure, heat radiation can be improved by fixing the ceramic substrate having the hybrid IC directly to the heat radiating fin 23.
Incidentally, the printed circuit board 25 is fixed to the case 24 by using screws 26. Similarly, the fin 23 is fixed to the case 24 and the printed circuit board 25 by using screws 27, 28. Accordingly, the heat radiating fin 23 contacts an inner wall of the case 24 when the fin 23 is fixed to the case 24 as shown in FIGS. 7A and 7B. Therefore, heat generated in the ceramic substrate 21 by semiconductor elements in the power IC is externally radiated from the case 4 through the fin 23. In addition, even when the case 24 holds several ceramic substrates, a whole dimension of the case 24 can be miniaturized by fixing the several ceramic substrates to the fin 23 in common.
Usually, a surface of the printed circuit board and each electrically connecting portion are covered and protected by a moisture-proof material such as a humid-sealing. The portion which needs a moisture-proof described above is covered by the moisture-proof material that is coated by spray and the like after the ceramic substrate 21 and the fin 23 are mounted on the printed circuit board 25. Then, the printed circuit board 25 is put in the case 24. Therefore, the moisture-poof material adheres to the fin 23 or the case 24 occasionally. FIG. 7C is a enlarged view showing a portion around a contacting interface between the case 24 and the fin 23.
Usually, moisture-proof material has a heat insulating characteristic. Therefore, in the case that a moisture-proof material K0 adheres to the interface between the case 24 and the fin 23, heat radiation of the device becomes worse because heat resistance between the case 24 and the fin 23 increases by the moisture-proof material K0.
To avoid adhering of the moisture-proof material to the interface between the case 24 and the fin 23, a rigorous process control or special structure is required. Thus, it may take much time to assemble the printed circuit board 25 and the case 24, or structure of the fin 23 or the case 24 becomes complicated.
In addition, the heat radiation of the device also become worse in the case that a contact surface of the case 24 or the fin 23 is deformed by an error in process, that is, in the case that the contact surface is not flat. This is because a contact area between the case 24 and the fin 23 is reduced. Thus, accuracy in processing of the case 24 and the fin 23 is required to make the contact surface flat.
This invention has been conceived in view of the background as described above and an object of the invention is to provide a semiconductor device in which heat radiating path is secured.
According to the invention, protrusions are formed on at least one of surfaces of a body member of a semiconductor device such as a case and a heat radiating member fixed to the body member. The heat radiating member contacts the body member through the protrusions. The protrusions serve as a heat radiating path.
Other objects, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings.